The reason is straightforward. The role that human and social capital plays in helping a person generate income in an advanced economy has increased over the last half a century. And over that same time, the primary institution for inculcating human and social capital has badly weakened.
Social scientists routinely find that individuals raised in intact families are generally better equipped to thrive in the economy. Today's 99% is teeming with tens of millions of Americans who were not raised in a stable home environment, and their earnings potential is compromised as a result.
If you had simply inherited your money from a rich, stable two-parent family (where dad's on his third wife and mom's on her second husband), you wouldn't be poor. Why can't you peons understand this? Because single women aren't putting all their babies up for adoption by rich families, you're doomed to a life of servitude and toil. You might as well get used to it because that's how the system works, and it's run by people who will do anything to perpetuate the system.
Besides, if you hippies are so smart, why haven't you fixed income inequality yet? Taxation clearly has failed, people have been paying taxes since America started and income inequality still exists, so clearly taxation on the rich cannot be any part of the solution. Immigration can't work, we've been allowing immigrants since the 1600's and look, income inequality! Failed policies of a worldview relegated to the dustbin of history!
If only rich people were allowed to have kids, that would fix this problem you know. Now stop using your sexual organs, you silly 99-percenters!